On 20/05/2021 18:00, Daniel Bristot de Oliveira wrote: > On 5/20/21 5:06 PM, Dietmar Eggemann wrote: >> On 20/05/2021 14:38, Daniel Bristot de Oliveira wrote: >>> On 5/20/21 12:33 PM, Quentin Perret wrote: >>>> On Thursday 20 May 2021 at 11:16:41 (+0100), Will Deacon wrote: >>>>> Ok, thanks for the insight. In which case, I'll go with what we discussed: >>>>> require admission control to be disabled for sched_setattr() but allow >>>>> execve() to a 32-bit task from a 64-bit deadline task with a warning (this >>>>> is probably similar to CPU hotplug?). >>>> >>>> Still not sure that we can let execve go through ... It will break AC >>>> all the same, so it should probably fail as well if AC is on IMO >>>> >>> >>> If the cpumask of the 32-bit task is != of the 64-bit task that is executing it, >>> the admission control needs to be re-executed, and it could fail. So I see this >>> operation equivalent to sched_setaffinity(). This will likely be true for future >>> schedulers that will allow arbitrary affinities (AC should run on affinity >>> change, and could fail). >>> >>> I would vote with Juri: "I'd go with fail hard if AC is on, let it >>> pass if AC is off (supposedly the user knows what to do)," (also hope nobody >>> complains until we add better support for affinity, and use this as a motivation >>> to get back on this front). >>> >>> -- Daniel >> >> (1) # chrt -d -T 5000000 -P 16666666 0 ./32bit_app >> >> (2) # ./32bit_app & >> >> # chrt -d -T 5000000 -P 16666666 -p 0 pid_of(32bit_app) >> >> >> Wouldn't the behaviour of (1) and (2) be different w/o this patch? >> >> In (1) __sched_setscheduler() happens before execve so it operates on >> p->cpus_ptr equal span. >> >> In (2) span != p->cpus_ptr so DL AC will fail. >> > > As far as I got, the case (1) would be spitted in two steps: > > - __sched_setscheduler() will work, then > - execv() would fail because (span != p->cpus_ptr) > > So... at the end, both (1) and (2) would result in a failure... > > am I missing something? Not sure. Reading this thread I was under the assumption that the only change would be the drop of this patch. But I assume there is also this 'if DL AC is on then let sched_setattr() fail for this 32bit task'. IMHO, the current patch-stack w/o this patch should let (1) succeed with DL AC.
